The present invention relates to aqueous surface treatment compositions, their preparation and their use.
The concept of using aqueous compositions for coating purposes has been known for several years. Moreover, the drive towards more environmentally friendly coatings containing low to zero amounts of volatile organic components (also referred to as V.O.C.""s) has added momentum to the development of water based coatings over traditional solvent based coatings.
Technical advances in the field of emulsion formulations have formed a basis for the commercial development of the commercial aqueous coating field that includes, for example, paints, stains and topcoat coatings. A ubiquitous aqueous coating composition is acrylic latex paint. Aqueous coatings based upon water-borne or emulsion formulations, are those whereby a polymeric resin (also referred to as a binder), pigments, and other additives are added to water with stirring until phase inversion occurs. High shear speeds and elevated temperatures are sometimes employed in order to achieve aqueous emulsion-based coatings. As well, emulsion-based aqueous coatings can be prepared by addition of one or more water-miscible solvents followed by stripping to remove the solvent from the final coating composition.
Polymeric resins in coatings act as binders to bind the pigment particles into uniform coatings and make the coatings adhere to the surface to which they are applied. They may also act as water-soluble thickening agents to provide thickening effects to the coatings. Other conventional aqueous coatings composition additives include, for example, emulsifiers, thickeners, humectants, curing agents, biocides, germicides, plasticizers, fillers and extenders.
If a film-forming coating is desired, coalescents can be added to aqueous coating compositions to temporarily lower the minimum film forming temperature, commonly referred to as the xe2x80x9cMFFTxe2x80x9d of a polymeric resin, allowing the coating composition to form a continuous film at a lower temperature than its Tg. The Tg, or glass transition temperature, of a polymer is a measure of the hardness and melt flow of the polymer. The higher the Tg, the less the melt flow and the harder the coating. Tg generally defines the onset of long range molecular motion wherein the polymer preserves the outward appearance of a solid but becomes rubbery and then tacky with increasing temperature and undergoes plastic flow and elastic deformation.
If a film-forming coating is desired, a polymer having a glass transition temperature at or near room temperature can be utilizied in the coating composition. In other instances, non-film forming aqueous coating compositions are desirous. For example, U.S. Pat. No. 4,094,841 teaches the use of a non-film forming latex coating prepared by emulsion polymerization for use with paper coatings and opacifying agents.
Despite their acceptance, current emulsion-based technologies used for the preparation of aqueous coatings have several drawbacks. Stability of emulsion-based aqueous coatings can be problematic and emulsion processes typically require surface-active agents, referred to as surfactants, to help stabilize the emulsions over long periods of time and a wide range of temperatures. Surfactants are also employed to inhibit foaming and to help disperse the pigments, or combinations thereof Conventional types of surfactants include anionic surfactants, non-ionic surfactants, cationic surfactants, amphoteric surfactants, or combinations thereof.
In aqueous coatings compositions, the rheology of the coating must be controlled in order to obtain proper flow of the surface treatment with a minimum of dripping or spattering. There are many types of thickeners, including polymeric water-soluble thickening agents, that may be added to emulsion based coatings to obtain a desired rheology. Thickeners such as cellulose ethers, alkali soluble latex copolymers, copolymers of acrylic and methacrylic acids and esters which have a portion of the hydrogen ions of the copolymer carboxyl group replaced with ammonium or alkali metals ions have been used as thickeners. Examples of thickeners are described in the patent literature, including U.S. Pat. No. 4,384,096 which discloses a pH responsive thickener comprising an ethylenically unsaturated carboxylic acid, at least one ethylenically unsaturated monomer and an ethylenically unsaturated surfactant copolymerizable therewith. Similar systems are disclosed in U.S. Pat. Nos. 5,874,495 and 4,138,381.
Another drawback of the current emulsion-based aqueous coating compositions is the detrimental effects of aqueous coating compositions on substrates that are of a porous or cellulose nature such as wood fibres. Grain raising, lap marks, distension and distortion may result after an emulsion-based aqueous coating composition has been applied due to the water-borne nature of the coatings.
Finally, the appearance of emulsion-based aqueous surface treatments can be a drawback. Emulsion-based aqueous coating compositions often retain an aesthetically undesirable turbid characteristic.
In order to compete with more conventional solvent-based coating systems, the aesthetic and physical properties of aqueous based coatings must be comparable. Alternative coating systems and compositions, and methods and apparatus for creating such systems and compositions are desirable.
In a first aspect of the present invention what is provided is an aqueous surface treatment composition comprising a polymeric water soluble thickening agent, water, and one or more than one basic neutralizing agents, wherein the percentages of components of said composition are selected in such a way that a viscous surface treatment composition is formed.
In accordance with a preferred embodiment of the invention, the aqueous surface treatment composition further comprises one or more than one colouring agent, or one or more than one polyol, or combinations thereof.
In accordance with yet another preferred embodiment of the invention, the polymeric water-soluble thickening agent has a Tg greater than 30xc2x0 C.
In accordance with yet another preferred embodiment of the invention the polymeric water soluble thickening agent comprises a crosslinked alkyl vinyl ether/maleic anhydride copolymer and the aqueous surface treatment composition is prepared, in part, by hydrolysis of the anhydride groups of the copolymer to the corresponding carboxylic acid groups, followed by neutralization using a basic neutralizing agent.
In accordance with yet another preferred embodiment of the invention, the aqueous surface treatment composition can be non-film forming upon application to a suitable substrate or film forming upon application to a suitable surface.
In accordance with yet another preferred embodiment of the invention, the aqueous surface treatment composition further comprises a polyol present at sufficient wt % such that, upon application of the surface treatment to a suitable surface, the surface treatment possesses a re-wettable edge.
In a second aspect of the present invention there is provided a method of providing a temporary surface treatment on a substrate comprising applying the surface treatment composition of the present invention to a substrate and allowing the composition to dry. As such, the surface treatment is subsequently removable upon application of water to the composition. Drying may take place under ambient temperatures or with the use of radiant heat.
In accordance with yet another preferred embodiment of the present invention, there is provided a method of providing a permanent surface treatment on a substrate by applying the surface treatment composition of the present invention to a substrate and allowing the composition to dry; followed by application of a sealant coating over the dried composition of the present invention. The sealant is allowed to dry to form a protective coating over the surface treatment composition. Drying may take place under ambient temperatures or with the use of radiant heat.
In a third aspect of the present invention there is provided a process for the preparation of an aqueous surface treatment composition, comprising the steps of adding a polymeric water soluble thickening agent to water, agitating the water and thickening agent solution until the polymeric agent is dispersed in the water and hydrolysed, and adding a basic neutralizing agent in sufficient quantity such that a viscous surface treatment composition is formed.
In accordance with another preferred embodiment of the invention, there is provided a process for the preparation of an aqueous surface treatment composition comprising the steps of preparing a first solution comprising water and a polymeric water soluble thickening agent; preparing a second solution comprising water and one or more than one basic neutralizing agents; and combining and mixing the solutions such that a viscous surface treatment composition is formed.
In accordance with yet another preferred embodiment of the invention, the second solution further comprises one or more than one colouring agent, or one or more than one polyol, or combinations thereof
In accordance with yet another preferred embodiment of the invention the first solution is acidic in pH and the second solution is basic in pH.
In accordance with yet another preferred embodiment of the invention, the water soluble thickening agent in the first solution is hydrolysed, and the hydrolysed solution is cooled to about 20xc2x0 C. to 60xc2x0 C., prior to mixing with the second solution.
In accordance with yet another preferred embodiment, the final surface treatment composition has a pH between 6 and 8. In accordance with yet another preferred embodiment, the final surface treatment composition has a pH of 7.
In a fourth aspect of the present invention there is provided an apparatus for the preparation and dispensing of composition including aqueous surface treatment compositions, comprising a plurality of mixing chambers for containing components of an aqueous surface treatment composition, each chamber having an outlet for passage of components of the composition from the mixing chamber; at least one mixing apparatus operatively connected to the mixing chambers so as to permit mixing of the components of the composition in the mixing chambers; a plurality of pumping chambers, each defining an inner volume, and each having at least one inlet to allow for passage of the components to the pumping chamber, and at least one outlet to allow for passage of components from the pumping chamber; a passageway extending from each of the mixing chambers to each of the pumping chambers for passage of the components of the surface treatment composition therethrough; a plurality of plungers, one plunger mounted in each of the pumping chambers, and each of the plungers being reciprocally movable toward and from the pumping chamber outlet, each of the plungers including a first portion sized to extend sealingly through the pumping chamber and permitting flow of the components outwardly through the outlets of the pumping chambers; a mixer assembly in fluid communication with the pumping chambers, and including mixing means for mixing the components of the aqueous surface treatment composition, and an outlet for passage of the mixed components from the mixer assembly; and wherein the components of the surface treatment composition are simultaneously mixed and dispensed.
In accordance with another preferred embodiment, the apparatus further comprises at least one heating apparatus contained within at least one of the mixing chambers for regulation of temperature of the components of the compositions.
In accordance with yet another preferred embodiment of the invention, the apparatus further comprises a drive mechanism operatively connected to the plungers to reciprocally drive the plungers movably through the pumping chambers. The internal volume of the pumping chambers are filled with the components of the surface treatment composition by force of suction by way of movement of the plungers away from the outlets of the pumping chambers, and the components of the surface treatment composition are displaced outwardly from the pumping chambers by force of the plungers towards the outlets of the pumping chambers. The drive mechanism can control the distance the plungers move through the pumping chambers thereby controlling the amount of components permitted to flow outwardly through the outlets of the pumping chambers to the mixer assembly.